study design of medical research by - alexandria …. shokeir study designs in medical research...

A.A. Shokeir

Study Design Of Medical Research

By

Ahmed A.Shokeir, MD,PHD, FEBU

Prof. Urology, Urology & Nephrology Center,

Mansoura, Egypt

A.A. Shokeir

Study Designs In Medical Research

Topics

Classification

Case – series studies

Case – control studies

Cross- sectional studies

Cohort studies

Interventional or Experimental studies

Summary

Exercises

A.A. Shokeir


Classification

• Subjects are observed

• No intervention

• Intervention is done

•Effect of interv. observed

-2 Basic Types

-Unclassified Type

Meta-analysis

Observational Interventional or

Experimental

A.A. Shokeir

Classification Observational Studies

4 Types

1) Case – series

2) Case – control

3) Cross – sectional

4) Cohort

A.A. Shokeir

Classification

Observational Studies

Initial Step Generate Hypothesis

Case – series Studies

The simplest design

Author describes some interesting observations

A small number of patients

Leading to generation of hypothesis

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Classification


Subsequent Step Test Hypothesis

- Hypothesis generated by case – series studies are further

investigated by the other 3 types of observational studies

depending upon 2 factors :

1- Duration of Time

2- Direction of Time

A.A. Shokeir


Types

1- Duration of Time

One time only

Cross – Sectional

Study

Extended period of time

•Case – control

•Cohort Longitudinal

A.A. Shokeir


Types


Forward Looking

Tomorrow

From risk factors to outcome

Cohort

Backward Looking

Yesterday

From outcome to risk factors

Case –control

Survey

Cross – sectional

Simultaneous Event

Today

A.A. Shokeir

Time relationship among observational studies

Cohort TODAY

Survey

Cross – sectional

Direction of Time

YESTERDAY TOMORROW Case-control

A.A. Shokeir

Time Relationship Among Observational

Studies

Question Terminology Time Study

What is happening?

What happened?

What will happen?

Survey

Retrospective

Prospective

Right now

In the past

In the future

Cross sectional

Case-control

Cohort

A.A. Shokeir

A.A. Shokeir


Classification


• No intervention



-2 Basic Types

-Unclassified Type

Meta-analysis


Experimental

A.A. Shokeir

Classification

Historical Sequential

Self – control Cross over

Interventional or Experimental

Noncontrolled Controlled

Parallel or

Concurrent

Randomized Nonrandomized

A.A. Shokeir

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Case –series Studies

Characters

A simple descriptive account of interesting

observations in a small group of patients.

Generates hypothesis.

There is no control.

Covers only a short time.

A.A. Shokeir


Advantages

1) Easy to write

2) May provide extremely useful information to

investigators designing a larger well - designed

study.

Disadvantages

Liable to many possible biases related to subject

selection and characteristics.

Should be viewed as hypothesis – generating and

not as conclusive

A.A. Shokeir


Example

Ghoneim and coworkers (2011) presented information in a

series of 20 adult patients with nocturnal enuresis. The

authors wanted to investigate the correlation between the

depth of sleep and the degree nocturnal enuresis. They

concluded that the relationship between the depth of sleep

and the degree of nocturnal enuresis is very strong.

A.A. Shokeir


Example

Small number 20 patients

Description of interesting observation Nocturnal enuresis

in adults.

Generates hypothesis correlation between degree of

enuresis and depth of sleep.

No control.

Covers a short time.

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General Information

Each study contains 2 important points

Start point Item under investigation

End point Outcome

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General information

Practical Example

Prolonged use of birth control pills

(BCP) may increase the risk of

development of breast cancer (Br Ca).

This example will be used to clarify the

different types of studies.

A.A. Shokeir

General Information

Practical Example

BCP vs. Br Ca

Item Under Investigation BCP

Outcome Br Ca

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Case-control Study

Definition:

The study contains 2 groups:

- Case group: contains the disease.

- Control group: dose not contain the disease.

Characters:

Always controlled

Always retrospective ( Backward looking )

Covers extended period of time (longitudinal)

Answers the question: “ What happened?”

A.A. Shokeir

Case – control Study

Practical Example

Ghoneim and associates (2011) compared 100 middle

aged women with breast cancer (Br Ca) versus 100

aged – matched women with no Br Ca. The authors

wanted to investigate the association between prior use

of birth control pills (BCP) and Br Ca. The authors

concluded that a strong association is observed between

prior use of BCP and Br Ca.

A.A. Shokeir

Case – control study design “Practical Example”

BCP users

BCP nonusers

BCP users

BCP nonusers

Cases

Breast- cancer

Controls

No Breast cancer

2011 2006

onset of study

Backward looking

Direction of inquiry

Question: How did the use of birth control pills (BCP) affect Breast cancer?

Time

A.A. Shokeir

Case – control study design

Exposed

Unexposed

Exposed

Unexposed

Cases

Controls

2011 2006

onset of study

Backward looking


Question “ What Happened”

Time

A.A. Shokeir

Case – control Study

At start of the study the authors already know

the outcome (Br Ca).

Then they study the item under investigation

(BCP).

The authors go backward in time to study the

correlation between the outcome (Br Ca) and

the item under investigation (BCP).

A.A. Shokeir

Case- control studies

Advantages

The quickest and least expensive.

Ideal for investigators who need preliminary

data prior to writing a proposal for a more

complete , expensive , and time – consuming

study.

Good choice for someone who needs to complete

a clinical research project in a short time.

A.A. Shokeir

Case – control Studies

Disadvantages

Of all study methods, they have the largest number

of possible biases or errors.

They depend completely on high quality

exiting records.

Many of the required data may not be

available at the time of writing article.

Great difficulty in choosing the controls who

are similar to the cases.

A.A. Shokeir

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Cross - sectional Studies

Names

Cross- sectional

Surveys

Epidemiologic

Prevalence

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Cross – sectional Studies

Characters

Analyze data collected on a group of

subjects at one time rather than over a

period of time.

Answer the question :

“ What is happening right now”

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Cross – Sectional Study Design

Practical Example

Middle - aged

women

With

Breast cancer

2011

Time

Onset of study

Question: “What is the prevalence of breast cancer

right now in middle - aged women?”

With

No Breast cancer

A.A. Shokeir

Cross – sectional Study Design

Subjects selected

for the study

With

outcome

Without

outcome

2011

Time

onset of study

No Direction of Inquiry

Question “What is happening?”

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The item under study (BCP) and the outcome

(Br Ca) are studied at the same time.

There is no direction of time.

Cross – sectional Study Design

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Cross – sectional Studies

Advantages

Similar to case – control studies being quick and

inexpensive

Disadvantages

Provide only a “ snapshot in time” of a disease or

process which may be misleading.

Indications

The best for determining the status of a disease or a

condition such as HIV in a given population.

Many people asked to participate in a survey

decline because they are busy or not interested. So

the sample may not be representative to the entire

population.

A.A. Shokeir

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Cohort Studies

Meaning of the word cohort

OXFORD DICTIONARY

A group of people united in supporting an idea,

a person , etc…..

A colleague

A companion

MEDIACL STUDIES

A cohort is a group of individuals who share a

common experience.

A.A. Shokeir

Cohort Studies

Concurrent

“ Typical”

Nonconcurrent

“ Historical”

“Data Base”

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Concurrent “ Typical” cohort studies

Individuals are observed over time to

determine their outcome.

It is called concurrent because individuals are

monitored concurrently over time.

A.A. Shokeir

Cohort Study Design Typical “concurrent”

Practical Example

Middle aged

women

Breast cancer

No Breast cancer

Breast cancer

No breast cancer

Already Using BCP

Already Not using BCP

Question: “ How will the use of birth control pills (BCP) affect prevalence of breast cancer in middle- aged women?

2016

Time

2011

Onset of study

A.A. Shokeir

Cohort Study Design

Typical “concurrent”

Cohort

selected for

the study

With outcome

Without outcome

With outcome

Without outcome

2016

Time

2011

Onset of study

Subjects already (exposed)

Control already (unexposed)

Direction of inquiry Question: “What will happen”?

Forward looking from now and forward

A.A. Shokeir

Concurrent “ Typical” cohort study

At start of the study the authors do not know the

outcome (Br Ca).

Then they study the item under investigation (BCP).

The authors go forward in time to correlate between

the item under investigation (BCP) and the outcome

(Br Ca).

A.A. Shokeir

Cohort studies

Concurrent

“ Typical”

Nonconcurrent

“ Historical”

“Data Base”

A.A. Shokeir

Historical (Non concurrent) Cohort Study design Practical Example

Records of

middle - aged

women

Breast cancer

No Breast cancer

Breast cancer

No Breast cancer

2011 Time

2006

Onset of study

BCP users

BCP

Nonusers

Forward looking from the past (2006) to the present (2011)


A.A. Shokeir

Historical Cohort (Nonconcurrent Cohort) Study Design

Records

selected for

the study

With outcome

Without outcome

With outcome

Without outcome

Forward looking from the past to the present time


2011

Time

2006

Onset of study

Subjects already (exposed)

Control already (unexposed)

A.A. Shokeir

Nonconcurrent “ Historical” cohort studies

“Data Base Research”

It is nonconcurrent because individuals are not

observed over time to determine the outcome, but the

outcome is determined at the same time the

individuals are assigned to the study.

It is still cohort study because at the time the

individuals are assigned to the study the investigator

does not know the outcome.

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Cohort studies

Indications

Because they are longitudinal and follow a

group of subjects over a prolonged period, they

are the design of choice for studying the risk

factors.

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Comparison of case – control and cohort studies

Cohort Studies

A cohort study begins by identifying a cohort that

posses the item under study (using BCP ) as well as a

cohort that does not possess that particular item ( NOT

using BCP ).

Then the frequency of disease (Br Ca) [the outcome] in

the 2 cohorts is obtained and compared.

A.A. Shokeir

Case-control study begins by the fact that the

investigator already knows that the study group (case

group) already has the disease (Br Ca) and the control

group DOES NOT have the disease.


Case – control Studies

Then the item under investigation (prior use of BCP )

is calculated in case versus control groups.

A.A. Shokeir

Concurrent cohort study 2016 2011

•100 women already using BCP

•100 women already not using BCP

•Start follow up Assessment of Br Ca

2011 Case - control study

2006

• Check files OF 2006

•100 women with Br Ca

•100 with no no Br Ca

•Assess for taking BCP

2011 Non concurrent cohort study 2006

•Check files of 2006

•100 women already using BCP

•100 already not using BCP

•Assess Br Ca


A.A. Shokeir


Direction of Time

Cohort TODAY

Survey

Cross – sectional

TOMORROW Case-control

Historical Cohort

YESTERDAY

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A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Interventional or Experimental Studies

General features

They include intervention. Then, the

results of intervention are observed.

Could be carried out on human “clinical”

or animals.

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Classification


Controlled Non controlled

Concurrent


Sequential Historical


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Randomized Clinical Trial (RCT)

Example

Group of Women

Study

Randomization

Control

Give BCP Don’t Give BCP

Probability of Br Ca

Follow-up

Intervention

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RCT Study Design

Practical Example

Middle aged

women

Breast cancer

No Breast cancer

Breast cancer

No Breast cancer

Give BCP

Don't give BCP

Randomization

2016

Assess Br Ca XXXXX

Give BCP or don't give BCP Onset of study

2011

Time

A.A. Shokeir

RCT Study Design

Subjects meeting

entry criteria

With outcome

Without outcome

With outcome

Without outcome

Experimental subjects

Controls

Randomization

Study outcome XXXXX

Intervention Onset of study

Time

2011 2016

A.A. Shokeir

Cohort Study Vs Randomized Clinical Trial

In cohort study there is no intervention. The item under study

is already existing and observation is done forward in time.

In RCT there is intervention through deciding to give or not to

give the item under study, then observation is done forward in

time.

In RCT decision to give or not to give the item under study is

taken by randomization.

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Randomized Clinical Trials (RCT)

Types of controls in RCT

1) Gold standard , reference standard , or

standard of care.

2) Placebo

3) Sham

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Randomized Clinical Trials

Types of Controls

1) Gold standard. “ passed the test of time”.

Treatment Modality:

Medication.

Surgical procedures.

Diagnosis Modality:

Radiological.

Endoscopic.

Histopathological

A.A. Shokeir


Types of Controls

2- Placebo

Used in pharmaceutical studies.

The drug under investigation is tested against a

phantom having the same shape , color , weight and

taste but having no effective material.

Placebo is important to nullify the psychological effect

of receiving the treatment.

A.A. Shokeir


Types of Controls

3- Sham Operations

Used in surgical experimental studies.

The animal is opened, the concerned organ is

identified and dissected, then the wound is

closed.

Sham operations is important to nullify the effect

of anesthesia, incision and closure of all wound

layers.

A.A. Shokeir


How To Do Randomization

The most common:

Closed envelop

Computer generated random tables.

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Indications

The best type to use when the objective is to

establish the efficacy of a treatment or a procedure.

Advantages

It is the gold standard or reference in medicine.

It provides the greatest justification for concluding the

cause and effect.

It is subject of least number of biases.

Disadvantages

Expensive

Needs a long time for follow up.

A.A. Shokeir


Types Patient Doctor

1- Open-label

2- Blind

3- Double Blind

X

X

X

A.A. Shokeir


Open-label Study

Example

A group of authors conducted a RCT of 100 patients

of benign prostatic hyperplasia. Patients were

randomized into 2 equal groups: group A received a

gold standard a-1a blocker (tamsulosin) and group B

received a new a-1d blocker (Naftopidil). All patients

know the type of treatment received. Follow-up was

carried out by the same doctors who already know the

type of treatment received by each patient.

A.A. Shokeir


Blind Study

Example

A group of authors conducted a RCT of 100 patients of

benign prostatic hyperplasia. Patients were randomized

into 2 equal groups; group A (50 patients) received α –

blocker (Tamsulosin) and group B (50 patients)

received placebo. All patients did not know the type of

treatment received. Patients were followed by the same

group of doctors conducting the study who know the

type of treatment received by each patient.

A.A. Shokeir


Double Blind Study Example

A group of authors conducted a RCT of 100 patients of

benign prostatic hyperplasia. Patients were randomized

into 2 equal groups; group A (50 patients) received α –

blocker (Tamsulosin) and group B (50 patients) received

placebo.

All patients did not know the type of treatment received.

patients of both groups were followed up by a doctor not

sharing in the study and was not aware of the kind

treatment received by each patient.

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Classification


Controlled Non controlled Controlled

Concurrent




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Trials With Self Controls

Description

The same group of patients is used for both experimental

and control options.

e.g. Before and after treatment.

Practical Example

The study by Ghoneim et al (2011) involved 100 patients with

lower urinary symptoms (LUTS) due to benign prostatic

hyperplasia (BPH). All patients were subjected to medical

treatment using α – blocker tamsulosin. The authors evaluated

their patients using AUA symptom score before treatment and

at 1 and 3 months after treatment. The authors concluded that

the use of tamsulosin improves the AUA symptoms score of

patients suffering from LUTS due to BPH.

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Classification



Concurrent




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Cross over study

2 groups: one experimental and one control

After a time, the experimental and control groups are

withdrawn from both groups for a “washout” period

during which both groups receive no treatment.

Experimental group is given treatment and control

group is given placebo.

The groups are then given the alternative

treatments; the first group receives placebo and the

second group receives the experimental treatment.

A.A. Shokeir

Crossover Study Design

X X X X X X X X Time Intervention Washout

period Intervention

Onset Of study

With outcome

Without

outcome

With outcome

Without

outcome

Subjects

meeting

entry

criteria

Controls

Experimental

subjects

Experimental

subjects

With outcome

Without

outcome

Controls

With outcome

Without

outcome

A.A. Shokeir

A group of authors conducted study including 100

patients with lower urinary tract symptoms (LUTs)

due to benign prostatic hyperplasia (BPH). The first

consecutive patients (group A) were given α – blocker

(Tamsulosin) and the subsequent consecutive 50

patients (group B) were given placebo. International

prostate symptom score (IPSS) was compared among

both groups after 6 weeks of continuous treatment.


Example

A.A. Shokeir

The treatment was stopped for 2 weeks and the type of

treatment in both groups was reversed: group A

patients who were receiving tamsulosin received

placebo and group B patients who were receiving

placebo received Tamsulosin. IPSS was compared

among both groups after 6 weeks of continuous

treatment.


Example (Cont.)

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Classification



Concurrent




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Trials with External or Historical Control

The third method for controlling experiments

is to use controls external to the study.

This may include:

Results of other investigators

Previous results of the same investigator

(Historical).

A.A. Shokeir

Trials with External or Historical Control

Example

A group of authors conducted a study

including 100 patients with BPH who were

treated by laser prostatectomy (study group).

At 1 year of follow-up the authors compared

the results of these 100 patients with the results

of other 100 patients with BPH who were

previously treated 2 years ago by the same

authors using the conventional transurethral

resection of the prostate (control group).

A.A. Shokeir

A.A. Shokeir


Classification


Experimental


• No intervention


•Effect of interv.observed

-2 Basic Type

-Unclassified Type

Meta – analysis

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Meta-analysis Study

Definition:

Combining data from 2 or more existing studies.

Importance

The most accurate way to draw a conclusion.

Helps overcome diversity of the results of

different studies.

Application

More appropriate to review articles.

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Masking

Masking of study subjects and investigators is an

important part of the assignment of patients in a RCT.

Single Masking “Blind Study”

Implies that the patient is not aware of which

therapy is being received.

Double Masking “Double Blind Study”

Implies that neither the patient nor the investigator

aware of group assignment.

A.A. Shokeir

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir


Classification


Experimental


• No intervention



-2 Basic Types

-Unclassified Type

Meta-analysis

A.A. Shokeir


4 Types

1) Case – series

2) Case – control

3) Cross – sectional

4) Cohort

A.A. Shokeir

Classification


Initial Step Generate Hypothesis


The simplest design

Author describes some interesting observations

A small number of patients

Leading to generation of hypothesis

A.A. Shokeir

Classification


Subsequent Step Test Hypothesis

- Hypothesis generated by case – series studies are further

investigated by the other 3 types of observational studies

depending upon 2 factors :

1- Duration of Time


A.A. Shokeir


Types

1- Duration of Time

One time only

Cross – Sectional

Study

Extended period of time

•Case – control

•Cohort Longitudinal

A.A. Shokeir


Types


Forward Looking

Tomorrow

From risk factors to outcome

Cohort

Backward Looking

Yesterday

From outcome to risk factors

Case –control

Survey

Cross – sectional

Simultaneous Event

Today

A.A. Shokeir


Direction of Time

Cohort TODAY

Survey

Cross – sectional

TOMORROW Case-control

Historical Cohort

YESTERDAY

A.A. Shokeir

Time Relationship Among Observational

Studies

Question Terminology Time Study

What is happening?

What happened?

What will happen?

Survey

Retrospective

Prospective

Right now

In the past

In the future

Cross sectional

Case-control

Cohort

A.A. Shokeir


Classification


Experimental


• No intervention



-2 Basic Types

-Unclassified Type

Meta-analysis

A.A. Shokeir

Classification

Historical Sequential



Noncontrolled Controlled

Parallel or

Concurrent


A.A. Shokeir

A.A. Shokeir


Topics

Classification




Cohort studies


Summary

Exercises

A.A. Shokeir

Exercises

1) Ghoneim and coworkers (2011) presented information in a

series of 20 patients who had been referred for evaluation of

stroke or transient ischemic attack. The authors wanted to

test the accuracy of a new method to predict peak systolic

velocity. They concluded that the new method is very

accurate.

The design of the above study is :

a- Case – series

b- Case – control

c- Cross sectional

d- Cohort

e- Randomized clinical trial

A.A. Shokeir

2) Ghoneim et al (2011) compared 100 patients who had

surgical site infection following laminectomy with 100

matched patients who developed no infection. Data were

retrieved from the patients files. The investigators found

that length of hospital stay and readmission rates were

greater with patients with infection. Furthermore,

postoperative incontinence was one of the risk factors

associated with the development of infection.


a- Cross sectional

b- Cohort

c- Case – control

d- Randomized clinical trial

e- Case – series

A.A. Shokeir

3) The study by Ghoneim et al (2011) involved patients who

underwent cholecystectomy. Patients were evaluated

preoperatively and at 1, and 3 months after

cholecystectomy. Changes such as abdominal pain,

flatulence and dyspepsia were compared in the same

patients before and after surgery.

The design in the above clinical study is :

a- Randomized clinical trial

b- Self - controlled clinical study

c- Clinical study with historical control

d- Crossover study

A.A. Shokeir

4) Ghoneim and coworkers (2011) designed a study to

determine the efficacy of immunotherapy with ant venom

for treating ant stings. The study involved a group of 68

adults who were allergic to ant stings; each subject was

randomly assigned to receive either venom immunotherapy

or a placebo. After a sting challenge in which any reactions

were recorded, the group originally on the placebo was

given the venom immunotherapy, and after a sufficient time,

they too were given a sting challenge.

The design of the above clinical study is :

a- Crossover study

b- Cross sectional study

c- Case – series study

d- Case – control study

A.A. Shokeir

5) Ghoneim et al (2011) wanted to compare prevalence of

infertility among married couples of Qatari and non

Qatari people. They sent a questionnaire to 5000 couples of

each group, of whom 2000 Qatari and 3000 non Qatari

people responded. The authors concluded that there was no

significant difference in the prevalence of infertility among

Qatari and non Qatari people.


a- Crossover

b- Cross – sectional

c- Case - control

d- Concurrent cohort

e- Nonconcurrent cohort

A.A. Shokeir

6- A group of authors wanted to study the association between

schistosomiasis and squamous cell carcinoma of the

bladder. The authors choosed 100 patients with squamous

cell carcinoma and 100 aged and sex matched people with

nonspecific cystitis from the database of the hospital. The

authors determined the percentage of patients with and

without schistosomiasis in both groups and found a

statistically higher proportion of schistosomal affection in

patients with squamous cell carcinoma.


a- Concurrent cohort

b- Nonconcurrent cohort

c- Case – control study


A.A. Shokeir

7- At 2011, a group of authors checked the files of 2006 and

chose 1000 smokers and 1000 aged and sex matched

nonsmokers. At 2011 the authors called the 2 groups and

examined them for the possibility of lung cancer . The

authors found a significantly higher prevalence of lung

cancer among smokers.


a- Case - control

b- Concurrent cohort

c- Nonconcurrent cohort


A.A. Shokeir

8- A group of authors choosed 500 patients with

hyperuricaemia and a similar number of age and sex

matched persons with normal serum uric acid. The

authors followed both groups for the possibility of

occurrence of urinary stones. Follow - up included renal

ultrasonography every 6 months. After 6 years of follow up

the authors demonstrated a statistically significant higher

incidence of renal stones in hyperuricaemic group.



b- Case - control

c- Concurrent cohort study

d-Nonconcurrent cohort study

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9- A group of 100 patients with lower ureteral stones were

randomly assigned to receive doxazosin (α blocker) (50

patients) or placebo (50 patients). Patients were followed up for

4 weeks by plain abdominal x- ray and ultrasonography.

Patients receiving α blocker had significantly higher proportion

of spontaneous stone passage compared with the placebo group.

The design of the above study is

a- Case - control

b- Randomized clinical trial



A.A. Shokeir

10- In which of the following study designs masking is

suitable to avoid selection bias:

a- Case - control studies

b- Concurrent cohort studies

c- Nonconcurrent cohort studies

d - Randomized clinical trial

A.A. Shokeir

A.A. Shokeir

Exercises

1) Ghoneim and coworkers (2011) presented information in a

series of 20 patients who had been referred for evaluation of

stroke or transient ischemic attack. The authors wanted to

test the accuracy of a new method to predict peak systolic

velocity. They concluded that the new method is very

accurate.


a- Case – series

b- Case – control

c- Cross sectional

d- Cohort

e- Randomized clinical trial

A.A. Shokeir

2) Ghoneim et al (2011) compared 100 patients who had

surgical site infection following laminectomy with 100

matched patients who developed no infection. Data were

retrieved from the patients files. The investigators found

that length of hospital stay and readmission rates were

greater with patients with infection. Furthermore,

postoperative incontinence was one of the risk factors

associated with the development of infection.


a- Cross sectional

b- Cohort

c- Case – control


e- Case – series

A.A. Shokeir

3) The study by Ghoneim et al (2011) involved patients who

underwent cholecystectomy. Patients were evaluated

preoperatively and at a1, and 3 months after cholecystectomy.

Changes such as abdominal pain, flatulence and dyspepsia

were compared in the same patients before and after surgery.

The design in the above clinical study is :


b- Self - controlled clinical study

c- Clinical study with historical control

d- Crossover study

A.A. Shokeir

4) Ghoneim and coworkers (2011) designed a study to

determine the efficacy of immunotherapy with ant venom

for treating ant stings. The study involved a group of 68

adults who were allergic to ant stings; each subject was

randomly assigned to receive either venom immunotherapy

or a placebo. After a sting challenge in which any reactions

were recorded, the group originally on the placebo was

given the venom immunotherapy, and after a sufficient time,

they too were given a sting challenge.

The design of the above clinical study is :

a- Crossover study

b- Cross sectional study

c- Case – series study

d- Case – control study

A.A. Shokeir

5) Ghoneim et al (2011) wanted to compare prevalence of

infertility among married couples of Qatari and non

Qatari people. They sent a questionnaire to 5000 couples of

each group, of whom 2000 Qatari and 3000 non Qatari

people responded. The authors concluded that there was no

significant difference in the prevalence of infertility among

Qatari and non Qatari people.


a- Crossover

b- Cross – sectional

c- Case - control

d- Concurrent cohort

e- Nonconcurrent cohort

A.A. Shokeir

6- A group of authors wanted to study the association between

schistosomiasis and squamous cell carcinoma of the

bladder. The authors choosed 100 patients with squamous

cell carcinoma and 100 aged and sex matched people with

nonspecific cystitis from the database of the hospital. The

authors determined the percentage of patients with and

without schistosomiasis in both groups and found a

statistically higher proportion of schistosomal affection in

patients with squamous cell carcinoma.


a- Concurrent cohort

b- Nonconcurrent cohort

c- Case – control study


A.A. Shokeir

7- At 2011, a group of authors checked the files of 2006 and

chose 1000 smokers and 1000 aged and sex matched

nonsmokers. At 2011 the authors called the 2 groups and

examined them for the possibility of lung cancer . The

authors found a significantly higher prevalence of lung

cancer among smokers.


a- Case - control

b- Concurrent cohort

c- Nonconcurrent cohort


A.A. Shokeir

8- A group of authors choosed 500 patients with

hyperuricaemia and a similar number of age and sex

matched persons with normal serum uric acid. The

authors followed both groups for the possibility of

occurrence of urinary stones. Follow - up included renal

ultrasonography every 6 months. After 6 years of follow up

the authors demonstrated a statistically significant higher

incidence of renal stones in hyperuricaemic group.



b- Case - control



A.A. Shokeir

9- A group of 100 patients with lower ureteral stones were

randomly assigned to receive doxazosin (α blocker) (50

patients) or placebo (50 patients). Patients were followed up for

4 weeks by plain abdominal x- ray and ultrasonography.

Patients receiving α blocker had significantly higher proportion

of spontaneous stone passage compared with the placebo group.

The design of the above study is

a- Case - control

b- Randomized clinical trial



A.A. Shokeir

10- In which of the following study designs masking is

suitable to avoid selection bias:

a- Case - control studies

b- Concurrent cohort studies

c- Nonconcurrent cohort studies

d - Randomized clinical trial

A.A. Shokeir

study design of medical research by - alexandria …. shokeir study designs in medical research...

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